Prior art electrophotographic printers are shown in Findley et al U.S. Pat. No. 3,999,168; Schomburg U.S. Pat. No. 4,000,486 and Rider et al U.S. Pat. No. 4,079,458.
These references describe not only the basic electrophotographic printer, but how that printer can be used, in an effective faction to print documents in either what is called portrait or landscape modes, see in particular FIGS. 2 and 3 of U.S. Pat. No. 4,079,458. Thus in portrait mode, the rows of alphanumerics or other symbols (hereinafter simply called symbols) are parallel to the short edge of the document whereas in landscape mode the rows of alphanumerics or symbols are parallel to the long edge of the document. These and other prior art devices appear to lack flexibility in that, at least insofar as they expressly describe it, successive scan lines, in the portrait mode, progress from left to right across the document. In the landscape mode, successive scan lines progress from the document top to the document bottom. There are circumstances in which additional degrees of flexibility are desired.
For example, and in connection with portrait mode printing, the scan lines described in the prior art are parallel to the long length of the document. However, the direction of the scan line (top to bottom or vice versa), and the direction in which scan lines progress are not necessarily fixed. There are at least eight different cases, in portrait mode printing, that can be defined (in four cases the scan lines are in the direction of the long dimension of the paper, and in four other cases the scan lines are in the direction of the short dimension of the paper). Regardless of the relationship between scan lines and the paper orientation, successive scan lines may progress either left to right or right to left. In addition, for left to right progression, the scan line itself can be directed either from top to bottom or bottom to top of the document. Similarly, for scan line progression from right to left, the scan line can extend either from top to bottom or bottom to top.
The same eight cases exist for landscape mode printing. Thus there are eight different possible combinations of scan line direction relative to symbol rows on the document, and the progression of successive scan lines relative to symbol row direction. These can be itemized as follows for convenience:
In one case the scan line is directed perpendicular to the symbol rows of the document, and is directed from the bottom of the document to the top, in this case successive scan lines progress from left to right.
In another case the only change is that the scan line is directed from top to bottom of the document.
In still another case, the scan line is also directed perpendicular to the symbol rows, from bottom to top of the document, but the successive scan lines progress right to left.
In still another arrangement, the scan line is also directed perpendicular to the symbol rows, and is directed from the top of the document to the bottom, successive scan lines progress from right to left.
Alternatively, the scan direction is parallel to the symbol rows. In a first such case, the scan line runs left to right and successive scan lines progress top to bottom.
In another arrangement, the scan line is directed right to left and successive scan lines progress top to bottom.
Still another arrangement has scan lines directed left to right and successive scan lines progressing bottom to top.
Finally, the last arrangement has scan lines directed right to left, successive scan lines progressing from bottom to top.
Prior art electrophotographic printers are divided into all points addressable (APA) and base line printers. Because of the flexibility of APA printers, there is often little constraint on the size or placement of symbols or graphics and as would be expected the flexibility renders these machines complex. Base line machines must reference all symbols or graphics to one of a number of conceptual, parallel base lines. Typically the font (or symbol definition) for base line machines includes symbols or graphics of a fixed size, usually at least the height of the font (the dimension perpendicular to the base line) is equal for all symbols. By reason of this constraint, the architecture of baseline machines is usually less complex.